This invention relates to vehicle brake systems, and more particularly to an apparatus and method for electrically augmenting the force applied through a push rod to a push rod actuated hydraulic master cylinder in a vehicle brake system.
Hydraulic brake systems for vehicles such as automobiles, trucks, buses, and motor homes, typically include a push rod actuated master cylinder for generating a hydraulic pressure that is transmitted through brake lines to actuate hydraulic brakes attached to the wheels of the vehicle, for slowing or stopping the wheels. It is desirable in such hydraulic brake systems for vehicles to include a power brake booster for augmenting the force applied to a brake pedal connected to the push rod, so that the amount of force that the operator is required to apply to the pedal for stopping or slowing the vehicle is significantly reduced.
Such power brake boosters have, in the past, typically utilized engine vacuum, hydraulic pressure, or pneumatic pressure to drive one or more pistons connected to the master cylinder for augmenting the force applied to the master cylinder via the push rod when the operator is pushing on the brake pedal. The engine vacuum is created by the action of a throttle mechanism, located inside the engine, that is used to cause vaporization and mixing of the fuel with combustion air. An alternate vacuum source in the form of an engine driven or electric vacuum pump may also be utilized. Pressure actuated power brake boosters require a source of pressure such as the power steering pump or a hydraulic boost pump for hydraulic systems or an air compressor for pneumatic systems.
Some modern vehicles are xe2x80x9cthrottle-less,xe2x80x9d however, and have no engine vacuum available for use in operating a power brake booster. In one form of such a vehicle, the vaporization and mixing of the fuel with combustion air is accomplished by judiciously regulating injection of the fuel through fuel injectors, and controlling the intake of combustion air by regulating the movement of engine intake valves.
In addition, the advent of xe2x80x9csteer by wirexe2x80x9d technology will eliminate the power steering pump as an available source of hydraulic power to operate a brake booster. The implementation of these technologies into future motor vehicles will require the addition of an electric or engine driven pump to provide a power source for the brake assist function.
What is needed, therefore, is an improved power brake booster that does not require engine vacuum or an auxiliary pressure or vacuum source to augment the force applied to the master cylinder via the push rod from the brake pedal.
Our invention provides a brake apparatus having an electric power brake booster, which does not require engine vacuum, for a push rod actuated hydraulic master cylinder.
In one form of our invention, the electric power brake booster includes an electrically powered actuator having an output shaft adapted for operative connection to the master cylinder, and an input for receipt of a signal indicative of force applied to the push rod. The electrically powered actuator augments the force applied to the push rod in response to the signal indicative of the force applied to the push rod. The booster may include a sensor for sensing force applied to the push rod and generating the signal indicative of the force applied to the push rod.
The electric booster may include a booster shaft supported within a housing for reciprocating movement along an axis. The booster shaft has an input end adapted for receiving an output end of the push rod and an output end adapted for operative connection to the master cylinder. The booster may also include an electric motor having an output shaft for delivering a torque, and a drive element including a ball screw operatively connected between the output shaft of the electric motor and the booster shaft for converting torque from the motor into axial force applied to the booster shaft. The booster may further include a motor brake operatively connected to the motor shaft for applying braking force to the motor shaft.
Our invention may also take the form of a method for operating a push rod actuated master cylinder, by connecting an electric brake booster to the master cylinder for augmenting a force applied to the push rod.
The foregoing and other features and advantages of our invention are apparent from the following detailed description of exemplary embodiments, read in conjunction with the accompanying drawing. The detailed description and drawing are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.